[PATCH v5] introduce macro spin_event_timeout()

[Benjamin Herrenschmidt]

> No, not udelay.  Or any delay for that matter.  If spinning on a
> condition, then there is no advantage to burning cycles with a
> udelay().  Those cycles may as well be used to keep testing the
> condition so the loop can be exited faster.  a udelay() would only
> serve to always make the busywait longer.

Well, there's a non-empty set of HW where polling as fast as you can
will effectively prevent it to make fwd progress...

Ben.